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RESEARCH PRODUCT

Thyroid Stimulating Antibodies Are Highly Prevalent in Hashimoto's Thyroiditis and Associated Orbitopathy

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Thyroid-associated orbitopathy (TAO) rarely occurs in patients with Hashimoto's thyroiditis (HT).There is evidence that TSH receptor stimulating antibodies (TSAb) play a role in the pathogenesis of TAO. In this report, the prevalence of TSAb in HT patients with and without TAO was studied.This is a longitudinal observational study.The study took place in an academic joint thyroid-eye clinic.A total of 1055 subjects were included.TSAb was measured with a Food and Drug Administration-cleared bioassay that uses Chinese hamster ovary cells expressing a chimeric TSH receptor and a cAMP response element-dependent luciferase. Results of TSAb activity were reported as percentage of specimen-to-reference ratio (SRR%, cutoff140%).We measured the association of TSAb with the risk of TAO in patients with HT.Of 700 consecutive and unselected patients with HT, 44 (6%) had overt TAO. Patients with HT+TAO were older (P.001), heavier smokers (P = .032), and clustered less with autoimmune diseases (P = .005). All healthy controls were TSAb negative. In contrast, serum was TSAb positive in 30/44 (68.2%) and 36/656 (5.5%, P.001) patients with HT+TAO and HT, respectively. Compared to patients with HT only, serum TSAb levels were higher in HT+TAO (median SRR%, 25th and 75th percentiles): 45, 35-65 vs 192.5, 115-455.3, P.001. Highest TSAb values were noted in patients with active and severe TAO vs those with mild and inactive TAO: 486, 392-592 vs 142, 73-192.5; P.001. The odds ratio of TSAb positivity for the risk of TAO adjusted for gender and age was 55.9 (95% confidence interval [CI], 24.6-127, P.0001), whereas the odds ratio per 10-fold change in TSAb SRR% (quantitative TSAb) was 133 (95% CI, 45-390, P.0001). The area under the receiver operating characteristic curve for qualitative and quantitative TSAb was 87.2% (95% CI, 80.6-93.8) and 89.4% (95% CI, 84.1-94.7), respectively.TSAb is strongly associated with TAO in HT and TSAb may contribute to the pathophysiology of TAO.